When someone dies in Japan what are the things they let float in the water?

Question:

What do they symbolize and what are they called?

Answer:

It's not common practice all over Japan, but in some reagion, people float paper dolls and/or paper lanterns on paper boats to rivers, where dead people's spirit reside in it and these paper boats take them to heaven.
It's called 精霊流し (Shourou nagashi) or 灯篭流し (Tourou Nagashi).